The ongoing development of data networks includes improving low-latency real-time media services such as a video conferencing. The rapid growth in the popularity of video conferencing services is indicative of demand for interactive data rich media services. However, despite extensive research and development in the areas of video encoding and networking technologies, it remains an elusive task to support low-latency interactive video over shared networks (e.g., public portions of the Internet) with satisfactory service quality.
Network congestion is often a factor that limits or deteriorates the perceptual quality of video conferencing services. Network congestion often occurs when a network node transmits a data flow at a rate that is greater than the available capacity of the network to handle the data flow on one or more network links. Network capacity is sometimes limited at data bottleneck points where multiple data flows demand access to a link over which bandwidth is limited relative to the instant demand of the multiple data flows. For example, cable modems serving multiple client devices are frequently bottleneck points. Data queues are used to gate throughput onto the link at such points to regulate traffic and avoid packet collisions. However, queues add delay and can overflow when an incoming rate of a data flow is greater than the output rate of the queue. In turn, the effects of network congestion include queuing delays, packet loss and difficulty in establishing new connections between network nodes. Due to such effects, incremental increases in traffic load can lead either to relatively small increases in network throughput or even to a reduction in network throughput for existing data flows.
Low-latency interactive real-time media services, such as video conferencing, also present additional challenges for congestion control. For example, often to a greater extent than for TCP, performance of a transport mechanism for such services is assessed on how well it: adapts to abrupt changes in available bandwidth; accommodates sluggish responses and output rate fluctuations of a transmit-side live video encoder; and avoids high queuing delays.
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